U.S. patent number 4,892,798 [Application Number 07/283,596] was granted by the patent office on 1990-01-09 for electrophoretic imaging metal-toner fluid dispersion.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Hsin-Hsin Chou, William M. Lamanna, Robin E. Wright.
United States Patent |
4,892,798 |
Lamanna , et al. |
January 9, 1990 |
**Please see images for:
( Certificate of Correction ) ** |
Electrophoretic imaging metal-toner fluid dispersion
Abstract
The present invention relates to toner fluid dispersions
comprising electrostatically charged colloidal elemental metal
particles dispersed in nonconductive organic liquid media of low
dielectric constant and containing a charge-inducing surfactant. In
other aspects, processes are disclosed for electrophoretically
depositing the colloidal elemental metal particles of the toner
fluid to produce nonconductive, continuous coatings or patterns and
methods of enhancing the coatings or patterns to make them
electrically conductive.
Inventors: |
Lamanna; William M. (St. Paul,
MN), Wright; Robin E. (St. Paul, MN), Chou; Hsin-Hsin
(St. Paul, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
23086779 |
Appl.
No.: |
07/283,596 |
Filed: |
December 13, 1988 |
Current U.S.
Class: |
430/38;
430/117.2; 430/118.6 |
Current CPC
Class: |
G03G
9/122 (20130101); H05K 3/1266 (20130101); G03G
9/12 (20130101); G03G 13/10 (20130101); H05K
2203/0517 (20130101) |
Current International
Class: |
G03G
13/06 (20060101); G03G 13/10 (20060101); G03G
9/12 (20060101); H05K 3/10 (20060101); G03G
013/10 () |
Field of
Search: |
;430/38,37,117,119 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Schaffert, R. M., "Electrophotography", The Focal Press, New York,
pp. 562-574, (1975). .
Turkevich, J., J. Gold Bull. 18, 86-91 and 125-131 (1985). .
Hirai, H., et al., J. Macromol. Sci.-Chem. A13, 663-649 and 727-750
(1979). .
Klabunde, K., et al., Proc. SPIE-Int. Soc. Opt. Eng. 821, 206-213
(1988). .
Klabunde, K., et al., Langmuir 2, 259-260 (1986). .
Klabunde, K., et al. ACS Symposium Series, 333 (High Energy
Processes Organomet. Chem.) 246-259 (1987). .
Klabunde, K. et al., Langmuir 3, 986-992 (1987). .
Kimura, et al., Bull Chem. Soc. Jpn. 56, 3578-3584 (1983); 57,
1683-1684 (1984). .
Ozin and Andrews, J. Phys. Chem., 90, 2929-2938 (1986). .
U.S. Patent Application Ser. No. 07/125,600. .
Buske, N., Colloids and Surfaces 12, 195-202 (1984). .
Shimoiizaka, J., et al., Fine Part. Process., Proc. Int. Symp.,
Samasundaran, P.Ed., AIME: New York 1980, pp. 1310-1324. .
Papirer, E., et al., J. Colloid and Interface Sci. 1983, 94,
207-219 and 220-228. .
Kilner, M., et al., IEEE Transactions on Magnetics 1984, 20,
1735-1737. .
Hoon, S. R., et al., J. Magn. Magn. Mater. 1983, 39, 107-110. .
Nakatani, I., et al., J. Magn. Magn. Mater. 65, 261-264
(1987)..
|
Primary Examiner: Goodrow; John L.
Attorney, Agent or Firm: Sell; Donald M. Kirn; Walter N.
Sherman; Lorraine R.
Claims
We claim:
1. A toner fluid dispersion comprising electrostatically charged,
colloidal elemental non-ferromagnetic metal particles dispersed in
an electrically nonconductive organic carrier liquid of dielectric
constant less than 3.5 and having a volume resistivity greater than
10.sup.12 ohm.cm, and an amount of a soluble surfactant effective
to charge and stabilize said dispersion, said metal particles
having sizes in the range of 1 to 100 nm.
2. The toner fluid according to claim 1 wherein said metal
particles are selected from the group of non-ferromagnetic metals
having atomic numbers in the range of 11 to 106.
3. The toner fluid according to claim 1 wherein said metals are
selected from the group consisting of aluminum, scandium, titanium,
vanadium, chromium, manganese, copper, zinc, gallium, germanium,
yttrium, zirconium, niobium, molybdenum, technetium, ruthenium,
rhodium, palladium, silver, cadmium, indium, tin, antimony,
lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium,
platinum, gold, thallium and lead.
4. The toner fluid according to claim 1 wherein said metals are
selected from the group consisting of copper, gold, iridium,
manganese, palladium, platinum, rhodium, silver, rhenium,
ruthenium, osmium, chromium, molybdenum, tungsten, indium, tin and
lead.
5. The toner fluid according to claim 1 wherein said metal is
selected from the group consisting of copper, gold, iridium,
manganese, palladium, platinum, rhodium, silver, rhenium,
ruthenium, osmium, chromium, molybdenum, tungsten, indium, tin, and
lead.
6. The toner fluid according to claim 1 wherein said metal is
selected from the group consisting of gold, silver, copper,
platinum, palladium, iridium, rhodium, rhenium, ruthenium, and
osmium.
7. The toner fluid according to claim 1 wherein said metals are
selected from the group consisting of gold, palladium, platinum,
silver, and copper.
8. The toner fluid according to claim 1 wherein said metal
particles have sizes in the range of 2 to 50 nm.
9. The toner fluid according to claim 1 wherein said metal
particles are present in the range of 0.001 to 1.0 percent by
weight in the carrier liquid.
10. The toner fluid according to claim 9 wherein said metal
particles are present in the range of 0.001 to 0.1 percent by
weight.
11. The toner fluid according to claim 1 wherein said carrier
liquid is selected from the group consisting of aliphatic and
aromatic hydrocarbons and halocarbons.
12. The toner fluid according to claim 1 wherein said surfactant is
selected from the group consisting of natural and synthetic
surfactants and combinations thereof.
13. The toner fluid according to claim 1 wherein said surfactant is
present in the range of 0.001 to 10.0 g/100 mL of carrier
liquid.
14. The toner fluid according to claim 1 wherein said metal
particles comprise a continuous or discontinuous layer of oxide on
a metal core.
15. The toner fluid according to claim 1 wherein said metal
particles further comprise a continuous or discontinuous outer
layer of said surfactant chemically or physically adsorbed
thereon.
16. The toner fluid according to claim 14 wherein said particles
further comprise a continuous or discontinuous outer layer of
surfactant chemically or physically adsorbed thereon.
17. The toner fluid according to claim 13 wherein said surfactant
is present in the range of 0.01 to 1.0 g/100 mL of carrier
liquid.
18. A method comprising the steps:
(a) providing the toner fluid dispersion according to claim 1, and
providing a dielectric or photoconductive substrate,
(b) electrophoretically and irreversibly depositing the charged,
colloidal, elemental metal particles of the toner fluid in a
continuous or imagewise fashion on at least one of the surfaces of
said substrate using standard electrographic techniques to provide
a nonconductive, colloidal, elemental metal coating thereon,
and
(c) optionally, in the case of a catalytically active colloidal,
elemental metal, subjecting the resulting colloidal metal coated
substrate to an electroless metal plating solution to induce
selective metal plating on the elemental colloidal metal coated
portions of the substrate surface, to provide a second elemental
metallic coating on said portions of the substrate surface which is
electrically conductive.
19. A catalytic article prepared according to the method of claim
18, steps (a) and (b).
20. A catalytic circuit prepared according to the method of claim
18, steps (a), (b), and (c).
21. A method comprising the steps:
(a) providing a toner fluid dispersion comprising electrostatically
charged, colloidal, elemental metal particles dispersed in an
electrically nonconductive organic carrier liquid of dielectric
constant less than 3.5 and having a volume resistivity greater than
10.sup.12 ohm.cm, and providing a dielectric or photoconductive
substrate,
(b) electrophoretically and irreversibly depositing the charged,
colloidal, elemental metal particles of the toner fluid in a
continuous or imagewise fashion on at least one of the surfaces of
said substrate using standard electrographic techniques to provide
a nonconductive, colloidal, elemental metal coating thereon,
and
(c) optionally, in the case of a catalytically active colloidal,
elemental metal, subjecting the resulting colloidal metal coated
substrate to an electroless metal plating solution to induce
selective metal plating on the elemental colloidal metal coated
portions of the substrate surface, to provide a second elemental
metallic coating on said portions of the substrate surface which is
electrically conductive.
22. A catalytic article prepared according to the method of claim
21, steps (a) and (b).
23. A printed circuit prepared according to the method of claim 21,
steps (a), (b), and (c).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toner fluid composition. In
another aspect, there is disclosed a process for
electrophoretically depositing the particles of the toner fluid to
provide coatings or patterns on a substrate. In a further aspect, a
method is provided for enhancing the coatings or patterns to make
them electrically conductive.
2. Description of the Background Art
Liquid developers or toners are commonly used in electrophoretic
development, particularly for applications where high image
resolution is desired. Toner fluids are typically comprised of
finely ground pigment particles dispersed in an insulating, organic
carrier liquid with charge control agents and/or surfactants added
to impart electrostatic charge to the particles and provide steric
stabilization toward flocculation. When an exposed electrographic
film bearing a latent, electrostatic charge image of a polarity
opposite to that of the dispersed pigment particles contacts the
toner fluid, the particles migrate to and deposit upon the image, a
process known as electrophoretic development.
Latent charge images can be formed using a variety of
electrographic processes including: (1) light or X-ray exposure of
an electrostatically charged photoconductor, (2) electrical
discharge resulting from application of a high voltage between
stylus and a conductive support covered with a dielectric receptor,
(3) ion projection, (4) electron beam printing, or (5) corona
discharge through a metallic mask, etc.
Liquid developers or toners must satisfy a number of requirements;
in particular, the concentration of excess ions must be very low in
order to prevent competition between the charged toner particles
and ions of the same polarity for development of the latent
electrostatic image. Volume resistivities greater than 10.sup.12
ohm.cm for the pure carrier liquid are normally required;
hydrocarbon and halogen-substituted hydrocarbon liquids are
commonly employed. Other factors, such as low dielectric constant
(less than 3.5), low viscosity and convenient melting point and
boiling point of the medium, colloidal particles with high
charge-to-mass ratios and mobilities, small particle size, adhesion
of the colloidal particles to the substrate, and stability toward
flocculation are also important. Typical particle compositions
include pigments such as phthalocyanine blue, monolite red R.S.,
nigrosene, zinc oxide, and carbon black as well as a number of
colored resin composites (i.e. latexes). For a more detailed
description of liquid toners and the liquid electrophoretic
development process, see R. M. Schaffert, "Electrophotography", The
Focal Press, New York, pages 562-574 (1974).
Chemical methods of producing colloidal metal dispersions via metal
salt reduction are well established, but entail use of aqueous or
polar organic media (high conductivity and dielectric constant). In
addition, reductive methods neccesarily produce ionic byproducts
which further increase the conductivity of the liquid medium. A
recent review dealing with the history, preparation, structural
features and properties of aqueous colloidal gold dispersions is
given by J. Turkevich in J. Gold Bull. 18, 86-91 and 125-131
(1985). Reductive methods of preparing colloidal metal dispersions
in alcohol or alcohol/water mixtures are described by H. Hirai, et.
al. in J. Macromol. Sci.-Chem. A13, 633-649 and 727-750 (1979).
Metal evaporation techniques for the production of stable colloidal
metal dispersions in polar organic liquids without added
surfactants have been described by Klabunde, K. et al. in Proc.
SPIE-Int. Soc. Opt. Eng. 821, 206-213 (1988); Klabunde, K. et al.,
Langmuir 2, 259-260 (1986); Klabunde, K. et al. ACS Symposium
Series, 333 (High Energy Processes Organomet. Chem.) 246-59 (1987);
Klabunde, K. et al., Langmuir 3, 986-992 (1987); and by Kimura et.
al. in Bull. Chem. Soc. Jpn. 56, 3578-3584 (1983) and 57, 1683-1684
(1984). Electrophoretic mobility studies have established that
dispersed metal particles in these polar media are
electrostatically charged. Although the charging mechanism is
uncertain, the electrostatic repulsion between particles is thought
to play an important role in stabilizing the dispersions. Unlike
dispersions prepared by reductive methods, the evaporative
techniques produce no ionic byproducts. However, conductivities and
dielectric constants of polar organic liquids are outside the
useful range for toner fluids. Similarly prepared dispersions in
nonpolar hydrocarbon media undergo rapid flocculation and
settling.
Ozin and Andrews in J. Phys. Chem., 90, 2929-2938 (1986) disclose
colloidal silver dispersions formed in liquid polyolefins such as
poly(butadiene), poly(isoprene) and squalene using metal
evaporation techniques.
Magnetic ferrofluids consisting of surfactant-stabilized
dispersions of colloidal, ferromagnetic metal or metal oxide
particles have been prepared in aqueous media as well as in polar
and nonpolar organic liquids. A variety of methods, including
prolonged grinding, precipitation, thermal or photochemical
decomposition of metal carbonyls and metal evaporation techniques
have been used in the preparation of these magnetic dispersions.
[See N. Buske, et al. Colloids and Surfaces 12, 195-202 (1984); J.
Shimoiizaka, et al. Fine Part. Process., Proc. Int. Symp.,
Somasundaran, P. Ed., AIME: New York 1980, pp. 1310-1394; E.
Papirer, et al. J. Colloid and Interface Sci. 1983, 94, 207-219 and
220-228; M. Kilner, et al. IEEE Transactions on Magnetics 1984, 20,
1735-1737; S. R. Hoon, et al. J. Magn. Magn. Mater. 1983, 39,
107-110; U.S. Pat. No. 4,576,725; U.S. Pat. No. 4,599,184; I.
Nakatani, et al. J. Magn. Magn. Mater. 65, 261-264 (1987)].
Magnetic developers for xerography have been patented (U.S. Pat.
Nos. 4,252,671 and 4,252,672) which consist of colloidal elemental
iron particles dispersed in organic liquid media and stabilized by
an active or passive polymer which is bound to the particle
surface. Use of these materials as developers is based, as in the
case of ferrofluids, on the magnetic properties of the dispersed
iron particles and their mobility in a magnetic field. A patent
covering dispersions of chromium, molybdenum, and tungsten useful
for the preparation of supported catalysts or optical recording
media is U.S. Pat. No. 4,252,675. In yet another disclosure, U.S.
Pat. No. 4,245,026 describes magnetically responsive toner
particles comprised of a low density, imbibitive polymer particle
impregnated within the pores of the polymer with iron, cobalt,
nickel or their respective oxides.
SUMMARY OF THE INVENTION
Briefly, the present invention provides a toner fluid comprising
electrostatically charged, colloidal elemental metal particles
dispersed in an electrically nonconductive organic carrier liquid
of low dielectric constant and a soluble surfactant in sufficient
concentration to charge and stabilize the colloidal metal
dispersion. Preferably, the colloidal metal particles are
nonferromagnetic, and more preferably they are noble metal
particles.
In another aspect, this invention relates to a process for
electrophoretically depositing the colloidal metal particles of the
toner fluid on a dielectric or photoconductive substrate to produce
nonconductive, metallic coatings on the substrate surface in the
form of continuous or discontinuous films which may be patterned
images.
In a still further aspect, in the case of a catalytically active
colloidal metal, the present invention relates to a process whereby
the colloidal metal coated substrate, wherein the metal coating is
continuous or discontinuous, is subjected to an electroless plating
solution to induce selective, catalyzed, metal plating in the
colloid coated areas to provide a second metal coating which is
electrically conductive, thus imparting electrical conductivity to
those areas.
More particularly, this invention provides a process comprising the
steps:
(a) providing the toner fluid of the invention, and providing a
dielectric or photoconductive substrate,
(b) electrophoretically depositing the charged, colloidal elemental
metal particles of the toner fluid in a uniform or imagewise
fashion on at least a portion of at least one surface of the
substrate using standard electrographic techniques to provide an
electrically nonconductive, colloidal, elemental metal coating
thereon, and
(c) optionally, in the case of a catalytically active colloidal
metal, subjecting the resulting colloidal elemental metal coated
substrate to an electroless metal plating solution to induce
selective metal plating on the colloidal elemental metal coated
portions of the substrate surface, to provide a second elemental,
metal coating on said portions of the substrate surface which is
electrically conductive.
Toner fluid compositions of this invention represent a departure
from the background art in that the dispersed phase consists of
elemental metal particles in the colloidal size range. Unlike the
traditional pigment particles used in toner fluids solely for
graphics applications, colloidal elemental metal particles offer
unique catalytic, electrical, magnetic, optical and biological
properties which form the basis for novel application concepts for
coated substrates in a host of different areas.
Stable dispersions of electrostatically charged, colloidal
elemental metal particles in liquid media of suitably low
conductivity and dielectric constant have not previously been
available for use as liquid toners in electrophoretic coating or
imaging. This is principally due to the lack of effective methods
of preparing stable dispersions of the required composition.
In this application:
"electrophoretic" means relating to the migration of suspended
particles in an electric field;
"toner fluid" or "liquid developer" or "liquid toner" means a
dispersion of small, charged particles in a fluid medium, which
respond to an electrostatic field in such a way as to make them
useful in electrophoretic coating and imaging;
"dispersion" means a two phase system where one phase consists of
small solid particles (i.e. in the colloidal size range, 1-100 nm)
preferably 2 to 50 nm distributed throughout and suspended in a
continuous, bulk, liquid phase;
"metal" means Periodic Table main group metals, transition metals,
noble metals, rare earth metals, and metalloids;
"stable" means that no more than 10 percent of the particles in the
colloidal dispersions settle over a period of 1 week under ambient
conditions of 25.degree. C. and 1 atmosphere pressure (760
Torr);
"electrically nonconductive", when it refers to the organic carrier
liquid, means that the pure liquid has a volume resistivity greater
than 10.sup.12 ohm.cm;
"electrically conductive", when it refers to the metallic coatings,
means that the conductivity of the coatings is greater than
10.sup.4 (ohm.cm).sup.-1 ;
"electrically nonconductive", when it refers to the metallic
coatings, means that the conductivity of the coatings is at most
10.sup.3 (ohm.cm).sup.-1 ;
"low dielectric constant" means a value less than 3.5 and
preferably less than 2.5 at 25.degree. C. and 1 kHz;
"surfactant" means a surface active agent or dispersing agent or
charge control agent which interacts with the surface of the
dispersed particles to provide electrostatic charge and in some
cases steric stabilization;
"substrate" means a material upon which a metallic coating is
deposited or image is developed;
"image" or "patterned image" means a reproduction or representative
reproduction of some original pattern of lines and/or shapes;
"liquid medium" or "carrier liquid" means an organic liquid used to
disperse the colloidal metal particles of the invention;
"soluble surfactant" means at least 1 milligram of surfactant
dissolves in 100 ml of the chosen organic carrier liquid; and
"without appreciable flocculation" means the number average
particle size as measured by photon correlation spectroscopy
increased by at most a factor of 10, preferably a factor of 5, and
most preferably a factor of 2, over a period of 3 months at a
temperature of 25.degree. C. and 1 atmosphere pressure.
Ferrofluids are known in the art. Their physical behavior and
applications derive from the ferromagnetic properties of the
dispersed particles and the extraordinary stability of the
dispersions in a magnetic field enables the entire fluid to flow or
become immobilized by an external magnetic field without
irreversible flocculation. In contrast, physical behavior and
utility of toner fluids relies on the electrostatic charge of the
dispersed particles and their tendency to migrate and irreversibly
flocculate in an external electric field, which, in turn, is
strongly dependent on factors such as conductivity and dielectric
constant of the medium. Despite certain similarities in
composition, ferrofluid and toner fluid performance are expected to
be mutually exclusive and dependent on the interplay of various
factors including surfactant and particle composition, surfactant
and particle loading, and the composition and physical properties
of the medium.
DETAILED DESCRIPTION AND SPECIFICATION OF THE INVENTION
The present invention provides unique toner fluid compositions
useful for the electrophoretic production of metallic coatings and
images. Toner fluids are comprised of electrostatically charged,
essentially pure, elemental, colloidal metal particles dispersed in
a nonconductive, organic carrier liquid of low dielectric constant
and a soluble surfactant in sufficient concentration to charge and
stabilize the colloidal metal dispersion. Generally the metallic
toner particles are negatively charged, but in certain instances
they are positively charged. Volume resistivity of the final toner
fluid dispersion is preferably greater than 10.sup.9 and more
preferably greater than 10.sup.10 ohm.cm.
For preparing the colloidal metal dispersions of the present
invention, known apparatus may be employed for generating metal
vapors which can be atomic metal vapors or a gaseous stream of
colloidal metal particles and contacting them with a dilute
solution of the surfactant in an organic carrier liquid.
Specifically, the gas evaporation reactor (GER) as described in
U.S. patent application Ser. No. 07/125,600 has proven to be
particularly useful for this purpose. Other reactor designs, such
as the Klabunde-style static reactor or a rotary reactor of the
Torrovap.TM. design (Torrovap Industries, Markham, Ontario, Canada)
may also be useful in certain instances, but are limited, by
comparison, in the scope of their utility. A complete description
of the three basic reactor designs and their use in the preparation
of colloidal metal dispersions is given in U.S. patent application
Ser. No. 07/125,600.
The variety of metals which can be used to prepare the stable
colloidal dispersions of this invention include transition metals,
noble metals and the rare earth metals and includes metalloids, for
example, aluminum and antimony, and main-group metals Stable,
colloidal metal dispersions can be prepared from a large number of
metals selected from the elements of atomic numbers 11-106. More
important metals in order of their atomic numbers are: aluminum,
scandium, titanium, vanadium, chromium, manganese, iron, cobalt,
nickel, copper, zinc, gallium, germanium, yttrium, zirconium,
niobium, molybdenum, technetium, ruthenium, rhodium, palladium,
silver, cadmium, indium, tin, antimony, lanthanum, gadolinium,
hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum,
gold, thallium and lead. Metals that are believed to be of
particular importance, all of which are non-ferromagnetic, for
purposes of this invention are: copper, gold, iridium, palladium,
platinum, rhodium, silver, rhenium, ruthenium, osmium, indium, tin
and lead.
Colloidal elemental metal particles of this invention may be
comprised of a single metal or combinations of two or more metals.
Mixed metal compositions may be produced in a number of ways,
including simultaneous or sequential metal evaporation from
multiple evaporation sources or evaporation of metal alloys from a
single source
Each of the colloidal elemental metal particles of the toner fluids
of the present invention has a metal core which is more than 99
weight percent, preferably more than 99.5 weight percent pure
metal. The metal core is usually crystalline, but may be amorphous
depending upon the conditions used in its preparation. The
elemental metal core may be surrounded by a thin surface coating of
metal oxide or metal salt formed by surface oxidation of the
elemental metal in air or by a component of the liquid medium. When
present, the metal oxide or salt coating can account for less than
20 mo)e percent, preferably 10 mole percent, most preferably 5 mole
percent, of the total metal content (metal plus metal oxide or
salt). In many cases, the particles are essentially free of any
oxide or metal salt coating. The extent of the oxide (or salt)
layer, when present, will depend on the ease of oxidation of the
particular elemental metal and the sample history (i.e., degree of
air exposure). Chemically or physically adsorbed surfactant can
form an extreme outer layer on the particles. Such a layer is
generally associated with (i.e., chemically or physically adsorbed)
the metal particles of the present invention. A layer of surfactant
on the metal particles serves to charge the particles in the
dispersion and may provide steric stabilization of the metal
particle dispersion toward flocculation. The surfactant and oxide
or salt layers may be continuous or non-continuous.
Size and distribution of the colloidal elemental metal particles is
similar for all of the evaporation techniques employed; particle
sizes ranging from 1 to 100 nm, but more commonly from 2 to 50 nm
have been identified by electron microscopy. Most preferably, a
mean particle size of 10 nm with a standard deviation of 1 to 6 nm
is achieved, preferably with a standard deviation less than 4 nm,
as determined by a combination of electron microscopy and photon
correlation spectroscopy. The small particle size and narrow
distribution provides high resolution in electrographic
imaging.
Limits on the maximum metal loadings in the toner fluid dipersions
are dependent upon the concentration of surfactant in the organic
carrier liquid. Limitations exist due to instability of the
dispersions toward particle aggregation or flocculation at high
metal concentrations. At the low surfactant concentrations most
commonly employed (0.01 to 1.0 g/100 ml of carrier liquid) in toner
fluids of this invention, metal loadings up to 1.0% by weight in
the organic carrier liquid, preferably in the range of 0.001 to
0.1% by weight, have been achieved without appreciable flocculation
of the dispersion over a period of months at room temperature under
ambient conditions.
Suitable organic carrier liquids useful in preparing toner fluid
dispersions of this invention must fulfill the normal requirements
of high volume resistivity and low dielectric constant previously
established for other liquid toners used in electrophoretic
development. Although firm limits have not been established, volume
resistivities greater than 10.sup.12, preferably greater than
10.sup.13, and most preferably greater than 10.sup.14 ohm.cm, and
dielectric constants less than 3.5, and preferably less than 2.5,
are acceptable. Furthermore, it is preferred that the carrier
liquid have a melting point of at most 15.degree. C., and a boiling
point between 60.degree.-300.degree. C. at 1 atmosphere pressure
and a viscosity less than 5 centipoise at 25.degree. C. Classes of
liquid media which satisfy these criteria and which can be employed
as carriers in toner fluid applications in the present invention
include: straight-chain, branched-chain, and cyclo-aliphatic
hydrocarbons such as petroleum oils, naphtha, ligroin, hexane,
pentane, heptane, octane, isododecane, isononane and cyclohexane;
aromatic hydrocarbons such as benzene, toluene and xylene; and
halocarbon liquids such as 1,1,2-trichloro-1,2,2-trifluoroethane,
trichloromonofluoromethane and carbon tetrachloride. Organic
carrier liquids particularly useful in the preparation of the toner
fluid dispersions of this invention, because of their high purity,
high volume resistivity, low dielectric constant, low viscosity,
and convenient boiling range are the isoparaffinic hydrocarbons
Isopar.TM. G (b.p.=156.degree.-176.degree. C) and Isopar.TM. M
(b.p.=207.degree.-254.degree. C.) (Exxon Company USA, Houston,
Tex.).
Utility of the colloidal metal dispersions of this invention as
toner fluids for electrophoretic development relies on the
electrostatic charge associated with the suspended metal particles
and the consequent mobility of the particles in an electric field.
Particle charging arises from the addition of surface active agents
(surfactants). According to present theory, surfactants interact
chemically with dispersed metal particles, causing specific
adsorption of ions a the particle surface. In toner fluid media of
low dielectric constant and low ion concentration, specific ion
adsorption from added surfactants is believed to be the principle
charge control mechanism. In addition to providing electrophoretic
mobility, the electrostatic charge on particles also stabilizes the
dispersions toward flocculation through mutual electrostatic
repulsion of particles of like charge. In the case of high
molecular weight surfactants, surface adsorbed species may also
provide steric stabilization of dispersions. Since the detailed
mechanism of charge control in liquid toners is not well
established and depends to a large degree on the particle surface
composition, no definitive rules regarding choice of surfactant are
available.
Surfactant compositions found to be effective as charge control
agents in toner fluid dispersions known in the art include natural
and synthetic materials and combinations thereof which can be
neutral or ionic. Natural materials include triglycerides such as
linseed oil and soybean oil, and fatty acids such as linoleic acid,
linolenic acid, oleic acid, and their combinations. Synthetic
surfactants generally provide superior toner fluid stability and
performance; these include homopolymers and copolymers of
vinyl-containing monomers such as: N-vinylpyrrolidone,
vinylalcohol, styrene, vinyltoluene, vinylpyridine, acrylates (i.e.
methylmethacrylate); block, graft or random copolymers such as
those comprised of the following monomer combinations:
styrene-butadiene, vinylchloride-vinyl ether, methacrylic acid
ester-N-vinylpyrrolidone, fatty acid-methacrylate ester,
styrene-allyl alcohol and alkylacrylate-styrene-butadiene;
polyesters of carboxylic acids (i.e. polydecamethylene sebacate,
alkyd resins); epoxy resins and phenolic resins (i.e. Novolaks);
functionally terminated homopolymers such as: epoxide or
amine-terminated polyolefins; ionic surfactants such as: copper
oleate, Aerosol.TM. TO (sodium dioctylsulfosuccinate),
triisoamylammonium picrate and aluminum octoate and mixtures or
combinations thereof. Other commercially available charge control
agents useful in the art are given in R. M. Shaffert,
"Electrophotography" (supra), pages 71, 72.
Specific surfactants found to be useful in producing toner fluid
dispersions of the present invention include epoxide terminated
polyisobutylenes: Actipol.TM. E6, E16, and E23 (Amoco Chemical Co.,
Chicago, Ill.); commercial oil additives: Lubrizol.TM. 6401 and
Lubrizol.TM. 6418 (The Lubrizol Corporation, Wickliffe, Ohio),
AMOCO.TM. 9250 (AMOCO Petroleum Additives Company, Naperville,
Ill.), and OLOA.TM. 1200 (Chevron Chemical Company, San Francisco,
Calif.); and hydrocarbon compatible hyperdispersants such as
Solsperse.TM. 17,000 (ICI Americas Inc., Wilmington, Del.). OLOA
1200, a low molecular weight polyisobutylene attached to a diamine
head group by a succinimide linkage, is the preferred surfactant
because of the stability and performance it imparts to the
resulting toner fluids.
Concentration of surfactant used in preparing colloidal metal
dispersions can have a dramatic influence on toner fluid
performance. Surfactant concentration levels that are too low
result in inadequate stability toward flocculation, whereas excess
surfactant can lead to high ion concentrations in the medium which
reduce the speed and efficiency of the development process In
general, surfactant concentrations between 0.001 and 10.0 g/100 mL
based on the total fluid, but preferably between 0.01 and 1.0 g/100
mL, can be used to prepare toner fluid dispersions of this
invention. With the surfactant OLOA 1200, concentrations between
0.01 and 0.12 g/100 ml in Isopar M or G produced toner fluids;
optimum developing speed and efficiency were attained at a level of
0.04 g/100 ml.
In another aspect of this invention, methods are provided for
electrophoretically depositing the colloidal metal particles of the
toner fluid on a dielectric or photoconductive substrate to produce
uniform, nonconductive, metallic coatings on a substrate surface in
the form of continuous films or patterned images. In the present
invention, it was convenient to use substrates in the form of thin,
2-dimensional, planar sheet constructions, although alternative
substrate constructions are possible. Suitable dielectric
substrates include virtually any nonconductive organic or inorganic
solid, particularly polymeric and ceramic materials readily
fabricated into thin films or other appropriate constructions.
Suitable photoconductive films may be of the organic or inorganic
type, such as those described by R. M. Schaffert in
"Electrophotography" The Focal Press, New York, 1975, pp. 60-69,
260-396.
Examples of useful substrate compositions include dielectric
polymers such as: Kapton.TM. polyimide (duPont de Nemours & Co.
Inc., Wilmington, Del.), polypropylene and polyethylene
terephthalate (PET); inorganic dielectric materials such as
aluminum oxide and silica-based glasses; and photoconductive film
constructions such as: Kodak Ektavolt.TM. Recording Film SO-102
(Eastman Kodak Co., Rochester, N.Y.) and
bis-5,5,-(N-ethylbenzo[a]carbazolyl)-phenyl methane (BBCPM) based
photoconductive films described in U.S. Pat. Nos. 4,337,305 and
4,356,244. One may use a wide range of alternative dielectric and
photoconductive materials as the substrates in the present
invention.
Electrophoretic deposition is achieved using known electrographic
coating and imaging techniques. These generally involve first
sensitizing or charging the substrate surface by, for example,
deposition of positive or negative ions generated in a corona
discharge, followed by development of charged areas of substrate
via the electrostatic attraction of the oppositely charged
particles of the toner fluid. Alternatively, an external electric
field may be applied to drive charged toner particles to the
substrate surface. A number of variations on these basic processes
are known in the art, but all basically rely on mobility of
electrostatically charged toner particles in an electric field to
achieve controlled deposition of particles on the substrate
surface. Coatings thus produced may be in the form of continuous
films covering the entire substrate surface or patterned images.
Patterned images are produced by selective charging of the
substrate surface to form a latent electrostatic image followed by
selective electrophoretic development of only the charged or
uncharged areas.
For the purpose of this invention, standard electrophotographic
equipment was used for producing colloidal metal coatings and
patterned images on a variety of substrates. A particularly useful
electrophotographic set-up consisted of the following components:
(1) a corona-discharge unit for depositing charge on the substrate
surface, (2) a projection exposure unit for generating a latent
electrostatic image on a photoconductive substrate, and (3) an
extrusion-type developing station for contacting the charged
substrate with toner fluid of the invention and providing
controlled colloidal metal deposition on the substrate surface
through application of a potential bias. Representative methods of
producing colloidal metal coatings or patterned images using this
equipment are included in the examples which follow.
Density of colloidal metal particles in the coatings produced via
electrophoretic deposition depends on a number of parameters
including substrate film thickness, corona-charging potential, bias
voltage applied to the developing station, and development time. In
the case of transparent substrates, relative metal loadings in the
coated areas were estimated from measured optical densities. For a
fixed surface potential, metal loadings decreased with increasing
substrate film thickness, thus limiting the practical scope of the
process to dielectric or photoconductive substrates in which the
dielectric or photoconductive layer is less than approximately 1270
micrometers (50 mil) thick and preferably less than 255 micrometers
(10 mil) thick. At the highest metal loadings generated on
ultrathin (6 micrometer) polyester film, colloidal metal coatings
were still nonconductive according to two-probe resistance
measurements indicating an absence of extended contacts between
metallic particles.
In one of the preferred embodiments of this invention, colloidal
metal particles were electrophoretically deposited on a BBCPM based
photoconductive film construction described in U.S. Pat. No.
4,337,305, Example 26, in the form of high resolution,
nonconductive, metallic images. High resolution imaging was
achieved by first charging the entire surface of the photoconductor
in a corona discharge and then selectively discharging the surface
by exposure to a projected image of a high resolution target to
form a latent electrostatic image. Development of the latent image
under a controlled bias potential using the metallic toner fluid
dispersion of the invention produced the corresponding colloidal
metal image. Nonconductive, metallic images with a resolution up to
240 line-pairs/mm or individual line widths of equal to or greater
than 2.0 micrometers have been obtained. Based on the average size
of the colloidal metal particles (about 10 nm), resolution in the
submicrometer range is expected to be feasible with more
sophisticated electrophotographic equipment.
In yet another aspect of this invention, methods are provided for
enhancing the electrophoretically deposited, nonconductive,
colloidal metal coatings and images via electroless metal plating.
In this process, immobilized colloidal metal particles function as
catalysts for promoting electroless metal plating. Thus,
electroless metal plating occurs selectively in those areas on the
substrate surface where colloidal metal has been deposited.
Enhanced coatings and images become completely metallized in the
electroless plating process and exhibit excellent electrical
conductivity. Furthermore, even at resolutions up to 150
line-pairs/mm, image enhancement and electrical conductivity is
achieved with negligible resolution loss.
Colloidal metals known to be useful as catalysts for electroless
plating include metals from Periodic Table Groups 8-11.
Particularly useful in terms of their catalytic activity are the
metals Cu, Ni, Ag, Au, Pt, and Pd. From the standpoint of a
desirable combination of cost, stability (toward oxidation or
flocculation), and catalytic activity, colloidal Pd appears to be
the metal of choice in this application.
Electroless plating solutions useful in this process have been
described in the prior art. These minimally consist of a solution
of a metal salt and a reducing agent in aqueous or organic media.
In an electroless plating process the metal in the metal salt is
catalytically reduced to its elemental form and deposited as such.
Salts of a variety of metals have been shown to be effective for
this purpose. Particularly useful are aqueous electroless plating
solutions of copper, nickel, and cobalt which are readily prepared
or are available from a variety of commercial sources and are
described in "Plating of Plastics with Metals" by J. McDermott,
Noyes Data Corporation, Park Ridge, N.J., pp. 62, 94, 177
(1974).
Metallic toner fluid dispersions of the present invention can be
used to prepare articles coated in a continuous or imagewise
fashion with colloidal metal. Colloidal metal coatings appear
continuous to the eye but when viewed with an electron microscope,
discrete metal particles can be seen. Articles bearing the
nonconductive, colloidal metal coatings can find applications in
areas of catalysis (i.e. electroless plating), optical or magnetic
recording and biomedical science. Electroless plated articles in
which the original colloidal metal coating has been enhanced and
made electrically conductive can find applications in the
electronics area as printed circuits or microcircuits or materials
for antistatic control. Other applications in the graphics
reproduction area for producing metallized graphics or in optical
devices for absorbing, reflecting or otherwise modulating various
types of radiation are also forseen.
Objects, features and advantages of this invention are further
illustrated by the following examples, but the particular examples
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this invention. All organic carrier liquids in the Examples had
volume resistivities qreater than 10.sup.14 ohm.cm and dielectric
constants less than 2.5.
EXAMPLE 1
This example describes a typical procedure for preparation of a
colloidal metal dispersion in a nonconductive organic liquid medium
of low dielectric constant containing a dissolved surfactant for
application as a liquid toner in electrophoretic coating and
imaging. Preparation of the dispersion was accomplished by metal
evaporation and transfer into the liquid medium using a Gas
Evaporation Reactor (GER).
In a GER reactor equipped with a direct drive mechanical vacuum
pump, gold metal was evaporated from a resistively heated, alumina
coated, tungsten crucible into a stream of N.sub.2 ; gas with a
flow rate adjusted such that the internal reactor pressure was
maintained at 10.0 torr. As the gold vapor was carried away from
the crucible in the gas stream, metal clustering occurred to form
colloidal gold particles. The stream of gold particles was bubbled
through a solution containing 0.022 wt % OLOA 1200 surfactant in
Isopar M at -40.degree. C. Gold particles captured by the solution
formed a dark purple, transparent dispersion containing 0.024% gold
by weight. The colloidal dispersion appeared to be indefinitely
stable under ambient conditions with no noticeable settling or
flocculation over a period of months. Analysis of the dispersion by
photon correlation spectroscopy revealed a mean number average gold
particle size of 10.0 nm with a standard deviation of 3.8 nm.
Presence of colloidal gold was confirmed by transmission electron
microscopy which showed highly crystalline particles with a primary
particle size ranging from 4-21 nm. Conductivity of the final
liquid dispersion was measured at 0.8.times.10.sup.-11
(ohm.cm).sup.-1 Electrophoresis measurements indicated that the
suspended gold particles were negatively charged with a zeta
potential of -230 mV (.+-.20%).
EXAMPLES 2-12*
The following samples were prepared by the method of Example 1
except that argon rather than nitrogen was used as the inert gas
stream:
______________________________________ Example Colloidal weight
weight Number Metal percent Surfactant percent
______________________________________ 2 Au 0.0183 OLOA 1200 0.02 3
Pd 0.0201 OLOA 1200 0.04 4 Ni 0.0039 OLOA 1200 0.04 5 Pt 0.0012
OLOA 1200 0.04 6 Cr <0.0100 OLOA 1200 0.03 7 Cu <0.0100 OLOA
1200 0.04 8 Pd <0.0100 AMOCO 9250 4.0 9 Pd <0.0500 LUBRIZOL
6418 0.03 10 Pd <0.0500 LUBRIZOL 6401 0.03 11 Ag <0.0100
AMOCO 9250 2.0 12 Pd 0.0052 Actipol E6 0.5
______________________________________ *Average metal particle size
determined by transmission electron microscopy and/or photon
correlation spectroscopy ranged from 5 to 15 nm; carrier liquid was
Isopar G.
EXAMPLE 13
This example describes a typical procedure for electrophoretic
deposition of continuous colloidal metal coatings on a dielectric
film substrate by application of an external electric field.
A 6 micrometer thick film of polyethylene terephthalate (PET, E. I.
duPont de Nemours & Co., Inc., Wilmington, Del.) was adhered to
a grounded aluminum plate by application of a thin layer of ethanol
at the film-aluminum interface. The entire assembly was passed
throuqh an extrusion type developing station commonly used in
liquid toner development using a colloidal gold dispersion in
Isopar M (prepared as in Example 1) as the toner fluid. With the
PET film in contact with the meniscus of the colloidal gold
dispersion, a negative potential of 300 V was applied to the
developing station such that the negatively charged gold particles
were repelled and driven to the surface of the polymer film. A
continuous colloidal elemental metal coating the width of the
developing station was produced. PET surface potential after
development was measured at -80 V with respect to the grounded
plate. Increasing the developing voltage or the development time
produced an increase in surface potential of the coated film and a
more dense colloidal metal coating on the PET surface. However,
even at the highest metal loadings, no electrical conductivity
could be detected by two probe resistance measurements.
EXAMPLE 14
This example describes a typical procedure for electrophoretic
deposition of continuous colloidal metal coatings on a dielectic
film substrate by charging the substrate surface in a corona
discharge.
A 6 micrometer thick film of PET was adhered to a grounded aluminum
plate as in the previous example. The entire assembly was passed
through a (+) DC corona discharge device in order to deposit a
positive charge on the PET surface with an initial surface
potential of 100 to 1000 V. Electrophoretic deposition of colloidal
gold or palladium coatings was accomplished by contacting the
charged surface with Isopar G dispersions of Examples 2 or 3, by
passing the film assembly through the extrusion developing station
at zero bias potential. This technique produced continuous
colloidal metal surface coatings on the PET surface. Density of the
colloidal metal coatings increased with increasing initial positive
surface potential; however, none of the coatings exhibited
measurable electrical conductivity.
EXAMPLE 15
This example describes a procedure for image-wise electrophoretic
deposition of colloidal metal patterns on a dielectric film
substrate at low resolution.
As in the previous example, a 6 micrometer thick film of PET was
adhered to a grounded aluminum plate. A high resolution, metallic,
Air Force target with patterned cutouts was placed on top of the
PET to mask the surface. The entire assembly was passed through a
(+) 6000 volt DC corona discharge to deposit a latent positive
charge pattern on the PET surface. After removing the metal mask,
the charge pattern was developed by exposure to a colloidal gold
dispersion in Isopar M (toner fluid prepared as in Example 1)
either by spraying with toner fluid or passing through the
extrusion type developing station as previously described.
Selective deposition of negatively charged gold particles on the
positively charged pattern produced a nonconductive colloidal metal
image. Maximum resolution was 4 lines/mm, the limit of the metal
target.
EXAMPLE 16
This example describes a procedure for production of high
resolution colloidal metal images on a photoconductive substrate
using standard electrophotographic techniques.
A film of BBCPM based organic photoconductor (prepared as in U.S.
Pat. No. 4,337,305, Example 26) was adhered to a grounded aluminum
plate and the surface of the photoconductor was charged with an
initial surface potential of (+)700 V by passage under a corona
discharge. Selective photodischarge to produce a latent positive
charge pattern was accomplished by projecting a 24X reduced image
of a high resolution target on the charged photoconductor surface
using a projection exposure unit. The latent charge pattern was
developed by contacting with a colloidal gold dispersion in Isopar
G containing 0.022 wt % OLOA 1200 (prepared as in Example 2) using
the extrusion developing station. Resolution of the final metallic
images depended on the applied developing bias potential and varied
from 150 line-pair/mm at 0 volts to 240 line-pair/mm at +200 volts.
Further increase in the developing bias potential did not increase
resolution, but decreased the optical density of the images.
Metallic images were purple to grey and exhibited negligible
conductivity according to 2-probe measurements.
EXAMPLES 17 and 18
These examples describe use of electrophoretically deposited metal
colloids on dielectric or photoconductive substrate surfaces as
immobilized catalysts for promoting selective electroless metal
deposition and the production of electrically conductive metallic
coatings and patterned images.
17. Continuous Electroless Plating of Alumina Plate
A colloidal gold coating was deposited from an Isopar G dispersion
(containing 0.022 wt % OLOA 1200 prepared as in Example 2) onto the
surface of a 635 micrometer (25 mil) thick fused alumina plate
according to the procedure described in Example 13. Bias potentials
up to -5000 volts were used. The gold coating was metallic grey in
appearance and nonconductive. Immersion of the plate in a
commercial electroless copper plating solution, CUPOSIT.TM. 328
(Shipley Company Inc., Newton, Mass.), at room temperature for 20
minutes produced a metallic copper film on the colloidal
gold-coated surface. No copper deposition occured on the gold-free
surfaces. A 2-probe resistance of approximately 10.0 ohms indicated
that the copper coating was electrically conductive. 18. High
Resolution, Image-Wise Electroless Plating of Photoconductive
Film
Colloidal gold line patterns with a maximum resolution of 150
line-pair/mm were produced on a film of BBCPM photoconductor using
the procedure described in Example 16. The initial images exhibited
no measurable electrical conductivity. Immersion of the imaged film
in a CUPOSIT 328 electroless plating solution for 20 minutes at
room temperature resulted in selective copper plating in the
colloidal metal coated areas. The final copper images displayed
enhanced electrical conductivity (2 probe resistance=approximately
10 ohms) with no loss of resolution.
Various modifications and alterations of this invention will become
apparent to those skilled in the art without departing from the
scope and spirit of this invention, and it should be understood
that this invention is not to be unduly limited to the illustrative
embodiments set forth herein.
* * * * *